Various studies are conducted on polylactic acids as biomass resins, and an attempt is made to find applications of the polylactic acids in a variety of fields. Particularly in the field of injection molding in which such a conventional polylactic acid is difficult to employ because of its lower crystallization rate, a polylactic acid excellent in heat resistance and moldability and having a higher crystallinity has been developed. As a result, the polylactic acid finds applications in a variety of fields, and an attempt has been made to employ the polylactic acid, for example, for household electric appliances and automotive components for which application of the polylactic acid was conventionally impossible.
Where the polylactic acid is employed for the household electric appliances and the automotive components, it is imperative to impart the polylactic acid with flame resistance. Halogen compounds and phosphorus compounds, which are highly effective for other resins, are known to be effective to impart a biodegradable resin with flame resistance. However, use of these compounds is not advantageous in consideration of environmental issues, toxicity and adverse effects on electronic devices, and alternative methods for the impartation of the flame resistance have been contemplated. For example, JP-A-8-252823, JP-A-2000-319532 and JP-A-2003-192925 disclose addition of a great amount of a metal hydroxide, use of a specific compound compatibilized with silicon oxide, and addition of a highly pure hydroxide compound or phosphorus compound, respectively, for the impartation of the flame resistance. Although a resin composition is imparted with flame resistance by the addition of a great amount of any of these inorganic compounds, the properties of the resin composition are significantly reduced, resulting in insufficient strength. In addition, the crystallization of the resin is not satisfactorily promoted, so that the resulting resin composition is poor in heat resistance. Further, JP-A-2004-190025 discloses that a flame-retardant polylactic acid excellent in heat resistance is provided by addition of a crystal nucleus agent as well as any of the aforementioned flame retarders. However, the disclosed crystal nucleus agent fails to sufficiently increase the crystallization rate, making it impossible to satisfactorily promote the crystallization of the resin during injection molding. Therefore, it is impossible to prepare a flame-retardant and heat-resistant resin excellent in moldability. In addition, the highly heat-resistant resin composition contains a great amount of a non-biodegradable organic compound and, hence, is less biodegradable.